A simplified view of H2A.Z structure and post-translational modifications. Bars indicate the major regions of divergence between H2A.Z proteins across species (green) and between H2A.Z and H2A (blue). The relative location of the nuclear localization signal (NLS) and regions of S. cerevisiae (Sc) H2A.Z (called Htz1) that mediate contact with the Nap1 chaperone and the SWR-complex (SWR-C) ATPase complex are also shown. All H2A.Z post-translational modifications identified so far are on the relatively divergent amino and carboxyl termini, so it is unclear whether each specific modification is invariably used to regulate variant function across species. Addition of post-translational modifications generally depends on the SWR complex, indicating that each modification occurs after the variant is assembled into chromatin [3, 5]. A major region of difference between H2A and H2A.Z is in the Loop 1 domain, which regulates interaction between the two H2A molecules in a nucleosome. This has led to the suggestion that nucleosome core particles can only be homotypic, containing either H2A or H2A.Z. However, hybrid nucleosomes containing H2A:H2B and H2A.Z:H2B dimers have been observed . The sequence of human H2A.Z-1, including the three residues that differ in H2A.Z-2, is also indicated.